Electrochemical analysis techniques are commonly used to generate medical data about biological fluids, such as blood and urine. Most electrochemical analyses of biological fluids are currently performed away from the patient care site at specialized analytical laboratories. The analytical process usually consists of the physician drawing one biological fluid sample from the patient for each test desired, sending the samples away to a centralized location for analysis, and waiting for the results to come back. The process is expensive, time consuming, and prone to communications error since both the sample and the results have to pass through several different people. Moreover, many samples have short shelf lives necessitating a rushed turnaround time that can foster mistakes. A delay in processing the sample might mean having to draw yet another sample from the patient. Further, it is advantageous to the patient that the test results are obtained as quickly as possible, since the patient can begin receiving treatment only after his condition has been properly diagnosed.
One alternative to sending fluid samples away for electrochemical analysis has been developed in the form of the automatic field analysis unit. A number of miniature field analysis units for automatically conducting electrochemical tests on biological fluids are known, such as those described in the claims and specifications of U.S. patent application Ser. No. 09/248,607 for a "Cartridge-Based Analytical Instrument with Optical Detector", U.S. patent application Ser. No. 09/248,614 for a "Cartridge-Based Analytical Instrument with Rotor Balance and Cartridge Lock/Ejection System", and U.S. patent application Ser. No. 09/248,737 for a "Cartridge-Based Analytical Instrument Using Centrifugal Force/Pressure for Mechanical Transport of Fluids". Typically, such miniature electrochemical testing units include disposable electrochemical test cells or cartridges in which two electrolytic solutions are connected by a salt bridge. One electrolytic solution is a reference solution while the other is the fluid sample to be analyzed. Probe electrodes connected to an electronic controller are introduced into the solutions and the electrical potential therebetween is measured.
It is important that the electrochemical data so generated by the analysis unit be accurate, since it will be used as the basis of a medical diagnosis. To this end, the analysis unit requires regular verification of its testing functions. The electrochemical testing function of the instrument may be checked by inserting a control cartridge containing standardized analytes having a known potential difference. This type of verification of function is known as testing with wet controls or wet testing. While wet controls offer an accurate measure of proper systems operation, they are inconvenient, expensive, and have limited reuse potential.
Another known way of verifying electrochemical function of the instrument is by inserting a control cartridge containing a battery and an electrical circuit to offer a predetermined voltage to the test probe electrodes of the analysis device. This type of verification of function is known as testing with dry controls or dry testing. While dry testing constitutes a quick and convenient one-point test, it is less effective than a test that exercises the instrument across a wide range of input conditions. There is therefore a need for a fast, convenient, inexpensive, and reusable test cartridge capable of providing a range of input voltage conditions to an automated electrochemical analysis instrument for verification of electrochemical testing functions. A means for satisfying this need has so far eluded those skilled in the art.